A method of characterizing a light source and a mobile device

ABSTRACT

A method of and a device for characterizing a light source and a method of selecting a replacement light source are provided. The method obtains ( 102 ) a first image of a light source in operation, obtains ( 106 ) a second image of the illuminated environment, and obtains ( 104, 108 ) first camera settings and second camera settings of the optical system and image processing system of the respective first and second camera at the respective moments in time that the first image and the second image was obtained. The first image, the second image, and the first and second camera settings are analyzed ( 110 ) to estimate characteristics of the light source. The characteristics of the light source may be used to propose a replacement light source and characteristics of the proposed replacement light source may be used to simulate the effect of the replacement light source on the illuminated environment.

FIELD OF THE INVENTION

The invention relates to methods and device which are capable ofcharacterizing a light source based on images obtained by a camera.

BACKGROUND OF THE INVENTION

It is required to know which type of light source is used in a lightingsystem in particular applications. For example, when lamps have to bereplaced with more energy-friendly lamps, one would like to replaceexisting light source with light sources that have about the same lightemission characteristics and, thus, knowledge about the currentlyinstalled light sources and light emitters is required. In otherapplications, a lighting system controls the light source such that aspecific, predefined, illumination pattern is obtained in theilluminated environment. A controller of such a lighting system has tohave some knowledge about the characteristics of the light source suchthat it is able to predict how the light source must be controlled toobtain the specific predefined illumination pattern.

In a first solution the characteristics of the installed light sourcesare manually provided to the controller of the lighting system. Everymoment in time that a light source is replaced, new light sourcecharacteristics must be provided to the controller. In a secondsolution, a light source is controlled in the operational mode and animage is taken of the illuminated environment to detect what theinfluence of the light source is on the environment and, possibly, toderive light source characteristics from the image. Although the secondsolution may be performed automatically and may even be performed everytime that the lighting system is switched on, it has specificdisadvantages: reflected light is used to characterize the light sourcesand, as such, the environment influences the determination of thecharacteristics of the light source. For example, when the wholeenvironment has a relatively dark color, the light intensity emitted bythe light source will be underestimated.

Published patent application WO2008/001259 discloses a method ofcontrolling a lighting system based on a target light distribution.Influence data is obtained for the light sources of the lighting systemwith a camera. The influence data comprises information in relation to aspecific light source of the lighting system and shows how theilluminated environment is influenced by the operation of a specificlight source. When the lighting system has to be controlled according toa target light distribution, the influence data is used to estimate howthe light sources must be controlled to obtain an illuminatedenvironment according to the target light distribution.

Patent application GB2453163A discloses a system for determining athree-dimensional representation of an object or scene. The systemprovides one or more light sources and comprises one or moretwo-dimensional image capture devices. In order to be able to determinethe three-dimensional representation of the object or scene,characteristics of the light source must be known. Light reflected bythe object or scene, as captured by the image capture devices, is usedto estimate the characteristics. As discussed previously, usingreflected light does not necessary lead to an accurate estimation of thelight source characteristics.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a method of characterizing alight source that more accurately estimates characteristics of the lightsource.

An aspect of the invention provides a method of characterizing a lightsource. A further aspect of the invention provides a method of selectinga replacement light source. Another aspect of the invention provides adevice for characterizing a light source. Advantageous embodiments aredefined in the dependent claims.

A method of characterizing a light source in accordance with the firstaspect of the invention comprises the stages of i) obtaining a firstimage of the light source in operation by means of a first camera, thefirst image is obtained from a first position (P1) in a first direction(210), ii) obtaining first camera settings, iii) obtaining a secondimage of an illuminated environment being illuminated by the lightsource by means of a second camera, the second image is obtained from asecond position (P2) in a second direction (214, 212) different from thefirst direction (210), iv) obtaining second camera settings, wherein thesecond camera settings represent parameters of an image processingsystem and of an optical system of the second camera used at the momentin time when the second image was obtained, and iv) analyzing the firstimage and analyzing the first camera settings to estimate firstparameters of the light source. The light source comprises a lightemitter for emitting light. The first camera settings represent theparameters of an image processing system and of an optical system of thefirst camera used at the moment in time when the first image wasobtained. The first parameters of the light source may relate tocharacteristics of light emitted by the light emitter. In the stage ofanalyzing the first image and analyzing the first camera settings,second image and the second camera settings are also analyzed toestimate second parameters of the light source and to more accuratelyestimate the first parameters of the light source, wherein the secondparameters of the light source relate to characteristics of a light beamemitted by the light source. The second parameters comprise informationrelating to a shape of the light beam.

The method according to the first aspect of the invention uses the firstimage, which directly images the light source in operation, as the basisfor characterizing the first parameters of the light source. Byobtaining the first image, it is prevented that other objects orsurfaces influence the light that is recorded in the first image suchthat the first image comprises reliable data about the light source.

Not all characteristics of the light source can be accurately estimatedon basis of the first image only. For example, one is not able to see onthe first image whether the light beam emitted by the light source isnarrow or wide. This information is present in the illuminatedenvironment, because in the illuminated environment the footprint of thelight beam is visible on surfaces of the illuminated environment andthis footprint can be translated into information that relates to theshape of the light beam such as, is the light beam narrow or wide, isthe light beam circular shaped or rectangular shaped, etc. Thus, byobtaining a second image much more and more reliable information aboutthe light source can be obtained. The information about the firstposition, the first direction, the second position and the seconddirection is also taken into account in order to be able to translateinformation in the illuminated environment into information that relatesto the light beam emitted by the light source. For example, perspectivechanges the shape of the footprint of the light beam and when the firstposition, second position and the first and second direction are known,the imaged shape of the footprint of the light beam can be transformedwith perspective correction techniques into the actual shape of thelight beam.

Thus, the obtaining of the first image and the second image, togetherwith obtaining the first camera settings and obtaining the second camerasettings, and by analyzing the information of these images and using thevalues of the settings, the method is capable of accurately estimatingparameters of the light source because more information is available.

Each image that is taken by a camera is up to a certain level influencedby the camera settings. When analogue images are taken, for example,shutter speed, aperture size, focal distance and film characteristics(ISO, type of film) determine how the light source is imaged. Whendigital images are taken, for example, shutter speed, aperture size,focal distance are still important camera settings that influence theimaging of the light source in the first image. In digital imaging alsoadditional image processing steps may be applied which influence theobtained first image. Examples of such additional image processing stepsare processing the raw data from the image sensor in accordance with aspecific ISO value, changing brightness and contrast and applying colorcorrections, etc. When the camera settings are known it is possible todeduct from the first image characteristics of the light that has beenreceived from the light source. For example, the shutter speed, aperturesize and ISO value may be used to calculate the light flux that had beenreceived from a specific portion of the light source. The color of aspecific portion of the first image, together with possible colorcorrections (or film characteristics) provide information about thecolor, color point, or color distribution that had been emitted by thelight source.

The terms light source and light transmitter are used to distinguish theactual component that emits the light from the whole package around thislight emitter. The light emitter is, for example, a light bulb, a lighttube, a LED, etc. The whole package around the light emitter maycomprise reflectors, optical elements, and/or other components of aluminaire which influence the light emission.

It is to be noted that an image sensor of the first camera is comprisedin the image processing system of the first camera.

Optionally, the first parameters may also relate to geometricalparameters of the light source. The first image itself may provideadditional information of the light source, such as size or shape of thelight source.

Optionally, the second camera is the first camera and the method furthercomprises the stage of repositioning the first camera after obtainingthe first image to the second position and redirecting the first camerain the second direction for obtaining the second image. This optionalembodiment may save hardware. When only one camera is available, stilltwo images can be made and only the repositioning and redirection isrequired as additional actions.

Optionally, the second position is substantially identical to the firstposition and the second direction is substantially opposite to the firstdirection. When a device is used which has at two opposite surfaces ofthe device a camera, this single device can be used to obtain the firstimage and the second image. Different types of mobile phones and tabletcomputers have two cameras at opposite sides and are, therefore, usefuldevices for executing the method according to the invention. The userhas to position the device at the first position and direct one cameratowards the light source in operation. Subsequently the device itselfmay automatically detect that it is directed towards a light source andmay automatically obtain the first image and the second image, or theuser provides a command to the device to obtain the first image and thesecond image. There is an additional advantage to obtain the first imageand the second image from about the same locations and in oppositedirections, because it makes the determination of light beam parameterseasier, for example, the footprint of the light beam that is imaged inthe second image is not altered because of the effect of differentperspectives in the different images.

In a preferred embodiment of the above discussed optional embodiment,the first and second position is within the light beam emitted by thelight source.

Optionally, characteristics of light emitted by the light emittercomprise at least one of: emitted light intensity by the light source,light emission spectrum of the light source, color point of the emittedlight, color temperature of the emitted light. Geometrical parameters ofthe light source comprise at least one of: shape of light emittingsurface of the light source, size of the light source, parameters ofvisible optical elements in the light source, characteristics of theluminaire in which the light source is provided. Visual optical elementsare, for example, visible reflectors, anti-glare lamellas, etc. Thecharacteristics of the luminaire comprise a shape, a size, a mountingand a type of luminaire.

Optionally, the characteristics of the light beam comprise at least oneof: spatial light emission distribution, spatial light intensitydistribution.

Optionally, the method further comprises the stages of i) analyzing thesecond image to determine whether the illuminated environment is alsoilluminated by additional light sources, the additional light sourcescomprising additional light emitters, ii) obtaining additional firstimages of the additional light sources, iii) obtaining additional firstcamera settings, wherein the additional first camera settings representthe parameters of the image processing system and of the optical systemof the first camera used at the moment of time when the additional firstimages were obtained. In the stage of analyzing the first image andanalyzing the first camera settings the additional first images and theadditional first camera settings are also analyzed to estimate theinfluence of the additional light source on the illuminated environmentof the second image such that the second parameters and/or firstparameters of the light source can be estimated more accurately. Thus,when more than one light source illuminates the environment, theinformation about the light source that is present in the second imagemay be distorted. If information of the additional light sources istaken into account, it is better possible to distinguish betweenlighting effects in the illuminated environment that originate from thelight source from lighting effects that originate from the additionallight sources. Consequently, the second parameters and also the firstparameters of the light source can be estimated more accurately.

Optionally, the step of analyzing the second image to estimate whetherthe illuminated environment is also illuminated by additional lightsources comprises the stages of: i) detecting an object in theilluminated environment, ii) detecting shadows around the detectedobject, iii) analyzing the detected shadows to estimate whether theilluminated environment is illuminated by additional light sources. Theoptional stages of this embodiment provide an heuristic to detectwhether other additional light sources are in operation at the moment intime when the second image was obtained. Heuristics are often powerfulalgorithms to obtain information with a certain accuracy level. In anadditional stage, the number of detected additional light sources may beprovided to a user who operates the first and/or second camera and aconfirmation is requested. It is to be noted that other heuristics mayalso be used to estimate whether the illuminated environment is alsoilluminated by additional light sources. It is to be noted that thestages i) and ii) may also be performed in another order, depending onthe used specific heuristics and specific algorithms.

Optionally, the method of characterizing a light source additionallycomprises the stage of analyzing the additional first images andanalyzing the additional first camera settings to estimate additionalparameters of the additional light sources, wherein the additionalparameters of the additional light sources relate to characteristics oflight emitted by the additional light emitters and relate to geometricalparameters of the additional light sources. It might be useful, incertain applications, to have also the additional parameters of theadditional light sources available. Furthermore, the additionalparameters may be used to better distinguish between lighting effectsoriginating from the light source and lighting effects originating fromthe additional light source in the second image.

Optionally, the light source is controllable in a first operational modeand a second operational mode, each one of the first operational modeand the second operational mode relates to a specific light emission,the light emission of the first operational mode is different from thelight emission of the second operational mode. The first image isobtained from the light source when the light source was operating inthe first operational mode. The method of characterizing a light sourceadditionally comprises the stages of: i) controlling the light sourceinto the second operational mode, ii) obtaining a further first image ofthe light source in operation in the second operational mode by means ofthe first camera, iii) obtaining further first camera settings, whereinthe further first camera settings represent the parameters of the imageprocessing system and of the optical system of the first camera used atthe moment in time when the further first image was obtained, and iv)analyzing the further first image and analyzing the further first camerasettings to estimate further parameters of the light source in relationto the second operational mode, wherein the further parameters of thelight source related to characteristics of light emitted by the lightemitter and relate to geometrical parameters of the light source. Thus,when, for example, the light source may be dimmed to a specific lightintensity level, or, when, for example, the light source can be switchedtowards emissions of different color distributions, this optionalembodiment provides means to estimate the characteristics of the lightsource when the light source is operating in different operationalmodes. Thus, the light source is better characterized. The optionalembodiment relates to a first and a second operational mode, but thelight source may operate in more than two operational modes and in anoptional embodiment, the characteristics of the light source areestimated for each one, or a sub-set of the plurality of operationalmodes.

Optionally, in the stage of obtaining the first image, stages ofobtaining the additional first images, and/or stages of obtaining thefurther first image comprises the stages of: i) instructing a user todirect the first camera to, respectively, the light source, theadditional light source or the light source operating the secondoperational mode, ii) detecting on basis of information of the imageprocessing system whether the amount of received light exceeds a minimumvalue, iii) obtaining the respective image when the amount of receivedlight exceeds the predetermined minimum value. This optional embodimentprevents that incorrect first images, incorrect additional first imagesand/or incorrect further first images are obtained because only if theminimum value is exceeded the probability that a light source inoperation is imaged is relatively high. The minimum value may bepredetermined or may be set dynamically, for example, in dependence ofthe average lighting conditions of the environment.

Optionally, the stage of analyzing the first image and analyzing thefirst camera settings to estimate the first parameters of the lightsource comprises the stages of: i) comparing the first image with imagesof light sources stored in a database to find an image of a light sourcethat is similar to the first image, the database also stores togetherwith the images of the light sources information about the parameters ofthe light source, ii) obtaining the first parameters from the databaseby obtaining parameters of the light source of the found image that issimilar to the first image. It might be that certain databases withimages of light sources are available. For example, a manufacturer oflight sources might provide such a database. Using such a database maylead with a relatively small effort to obtaining very accurate firstparameters (assuming that the database comprises accurate information).It is to be noted that, as discussed previously, in the stage ofanalyzing the first image and analyzing the first camera settings toestimate the first parameters of the light source, specific techniquesare used, such as specific optical calculations to estimate the lightintensity and/or the color of the received light and image recognitiontechniques to estimate geometrical parameters of the light source. Thisoptional embodiment may be used in addition to the specific techniquesand the data obtained from such techniques is used to find the mostsimilar image of a light source in the database. Alternatively, thisoptional embodiment may be used instead of applying the specifictechniques.

Optionally, the first camera is also configured to image the lightsource in the infrared spectral range to obtain a heat signature of thelight source and wherein, in the stage of analyzing the first image andanalyzing the first camera settings to estimate the first parameters ofthe light source, the heat signature is also analyzed to obtain furthercharacteristics of the light source which relate to the operationalconditions of the light source. Additional characteristics of the lightsource may be obtained from the heat signature and by using such a heatsignature the light source may be characterized more accurately.

Optionally, the first camera and/or the second camera are hyper spectralcameras. Conventional digital cameras use an RGB sensor array thatcreates an image which is a representation and estimation of theelectromagnetic waves that are received in the spectrum that is visibleto the human naked eye. A hyper spectral camera collects and processesinformation in more ranges of the complete electromagnetic spectrum andin narrower spectral bands. A hyper spectral camera generates, inspecific embodiments, different images for different spectral ranges.Hyper spectral cameras are capable of collecting more information and ifmore information is obtained, characteristics of the light source can beestimated more accurately.

According to a further aspect of the invention, a method of selecting areplacement light source is provided. The method comprises the stages ofthe method of characterizing a light source and further comprises theadditional stages of: i) selecting from a list of replacement lightsources and/or replacement light emitters a replacement light sourceand/or a replacement light emitter, wherein the replacement light sourceand/or the replacement light emitter have at least one parameter that issimilar to one of the first parameters and/or the second parameters ofthe light source, ii) proposing the selected replacement light sourceand/or the selected replacement light emitter to a user. These optionaladditional stages may be used in an automatic system which proposes tothe user a list of replacement light emitters and/or the replacementlight sources for the light source characterized. Thereby it has beenprevented that the user has to keep track of which specific types oflight sources are installed and/or that the user must manually comparecharacteristics of the installed light sources with availablereplacement light emitters and replacement light sources. Thus, thisoptional embodiment is relatively user friendly. The list may beretrieved from a database. For example, when a manufacturer of lightemitters and light sources provides a database with available lightemitters and light source, it is advantageous to use this database inthe method of characterizing a light source to select from thisparticular manufacturer a replacement light emitter or light source.

Optionally, the stage of selecting the replacement light source and/orthe replacement light emitter also takes into account the furtherparameters of the second operational mode of the light source. When thelight source may operate in different operational modes, it would benice to select a replacement light source and/or a replacement lightemitter which also has different operational modes with similarparameters. This optional embodiment enables a selection of areplacement light source/light emitter which has several operationalmodes, at least some of them being similar to operational modes of thelight source.

Optionally, the method of characterizing a light source comprises thestages of simulating an influence of the selected replacement lightsource and/or the selected replacement light emitter on the illuminatedenvironment. The illuminated environment is the environment that isimaged in the second image. The simulating of the influence of theselected replacement light source and/or the selected replacement lightemitter on the illuminated environment comprises creating an adaptedsecond image showing the influence of the selected replacement lightsource and/or the selected replacement light emitter on the environment.The adapted second image is presented to the user. This optionalembodiment is in particular user friendly when the selected replacementlight source and/or the selected replacement light emitter does notexactly have the same first parameters and/or the same second parametersas the light source, because the user now is provided with additionalinformation which assists him to judge whether the differences areacceptable or not.

Optionally, the selected replacement light emitter and/or the selectedreplacement light source may operate in a third operational mode and ina fourth operational mode. In each one of the third operational mode andthe fourth operational mode, the selected replacement light emitterand/or the selected replacement light source emits specific light. Thelight emission of the third operational mode may be different from thelight emission of the fourth operational mode. The obtained adaptedsecond image may relate to the third operational mode of the selectedreplacement light source and/or the selected replacement light emitter.The method now further comprises the stages of i) simulating aninfluence of the selected replacement light source and/or the selectedreplacement light emitter on the environment, the simulation relates tothe operation of the selected replacement light source and/or theselected replacement light emitter in the fourth operational mode, ii)creating a further adapted second image showing the result of thesimulating of the influence, iii) presenting the further adapted secondimage to the user. This optional embodiment provides the user withadditional information about what may be the influence of additionaloperational modes of the selected replacement light source and/or theselected replacement light emitter, and is, thus, user friendly.

According to another aspect of the invention, a computer program isprovided which comprises computer program code adapted to perform thestages of the method of characterizing a light source or of the methodof selecting a replacement light source when the computer program is runon a computer. Optionally, the computer program is embodied on acomputer readable medium.

According to a further aspect of the invention, a downloadableapplication for a mobile computing device is provided. The downloadableapplication comprises a computer program comprising computer programcode adapted to perform the stages of the method of characterizing alight source or of the method of selecting a replacement light sourcewhen the computer program is run on a processing unit of the mobilecomputing device. The mobile computing device is, for example, a smartphone or a tablet computer.

According to another aspect of the invention, a device forcharacterizing a light source is provided. The device comprises a firstcamera, a data storage and a processing unit. The first camera comprisesan image processing system and an optical system of which, whileobtaining an image with the first camera, parameters are adjusted toobtain the image of an imaged object or environment. The data storagesstores a computer program comprising computer program code adapted toperform the stages of the method of characterizing a light sourceaccording to any one of the above discussed embodiments of this methodor the stages of the method of selecting a replacement light sourceaccording to any one of the above discussed embodiments of this method.The processing unit is coupled to the data storage and to the firstcamera and is configured to execute the computer program stored on thedata storage. Optionally, the device is a mobile device.

The device according to the second aspect of the invention provides anapparatus to a user which may be used to characterize a light source.The devices assist in automatically characterizing light source.Further, when the device is a mobile device, it does not take a lot ofeffort to carry the device to the location where a light source must becharacterized, for example, when the light source must be replaced.

The parameters of the first camera may be automatically adjusted by thefirst camera, and/or one or more of these parameters of the first cameramay be adjusted by the user of the device. For example, the user mayselect the ISO value, or the user may use a zoom function to adjust thefocal point of a lens of the first camera.

Optionally, the computer program is stored in the device on the datastorage such as, for example, a hard disk, volatile or non-volatilememory, etc.

Optionally, the device comprises a second camera and optionally thesecond camera comprises an image processing system and an optical systemof which, during obtaining an image with the first camera, parametersare adjusted to obtain a quality image of an imaged object orenvironment the image processing system may be shared with the firstcamera. It is to be noted that when the device only comprises a firstcamera, the first image and the second image may be obtained placing thefirst camera first at the first position in the first direction andthereafter repositioning the first camera towards the second positioninto the second direction for obtaining the second image.

Optionally, the device comprises a user interface to provideinstructions to the user of the device and to present images to theuser.

Optionally, the processing unit is also configured to execute a furthercomputer program which comprises instructions to instruct via the userinterface of the device a user of the device to obtain the first imageof the light source with the first camera and to present the obtainedimage to the user. The provision of instructions to the user assists theuser in the operation of the device such that the obtained first imagecorrectly images the light source.

Optionally, the further computer program also comprises instructions toinstruct the user to direct the device in a substantially oppositedirection to obtain the second image of the illuminated environment andto present the obtained image to the user. The provision of instructionstherefore assists the user in executing the different stages of thevarious methods as described above.

Optionally, when the processing unit of the device also determines areplacement light source or replacement light emitter and when theprocessing unit also simulates the influence of the replacement lightsource or replacement light emitter to obtain an adapted second image,the device may be configured to present the adapted second image on adisplay of the user interface of the device.

The device according to the second aspect of the invention provides thesame benefits as the method of characterizing a light source accordingto the first aspect of the invention and has similar embodiments withsimilar effects as the corresponding embodiments of the method.

These and other aspects of the invention are apparent from and will beelucidated with reference to the embodiments described hereinafter.

It will be appreciated by those skilled in the art that two or more ofthe above-mentioned options, implementations, and/or aspects of theinvention may be combined in any way deemed useful.

Modifications and variations of the method, and/or of device, whichcorrespond to the described modifications and variations of the methodcan be carried out by a person skilled in the art on the basis of thepresent description.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 schematically shows a method of characterizing a light source,

FIG. 2 schematically shows a light source in an environment that itilluminates and schematically shows cameras for obtaining a first andsecond image,

FIG. 3 a schematically shows a first image of a light source,

FIG. 3 b schematically shows a second image of an illuminatedenvironment,

FIG. 4 a schematically shows a second image of an environment that isilluminated by two light sources,

FIG. 4 b schematically shows optional stages for the method of theinvention,

FIG. 5 a schematically shows optional additional stages for the methodof the invention,

FIG. 5 b schematically shows optional additional stages for the methodof the inventions,

FIG. 6 a schematically shows a further first image,

FIG. 6 b schematically shows an adapted second image, and

FIG. 7 schematically shows an embodiment of a mobile device.

It should be noted that items denoted by the same reference numerals indifferent Figures have the same structural features and the samefunctions, or are the same signals. Where the function and/or structureof such an item have been explained, there is no necessity for repeatedexplanation thereof in the detailed description.

The Figures are purely diagrammatic and not drawn to scale. Particularlyfor clarity, some dimensions are exaggerated strongly.

DETAILED DESCRIPTION

A first embodiment is shown in FIG. 1. FIG. 1 schematically shows amethod 100 of characterizing a light source. The method comprises thestages of: i) obtaining 102 a first image of the light source inoperation by means of a first camera, ii) obtaining 104 first camerasettings, wherein the first camera settings represent the parameters ofan image processing system and of an optical system of the first cameraused at the moment in time when the first image was obtained, and iii)analyzing 110 the first image and analyzing the first camera settings toestimate first parameters of the light source, wherein first parametersof the light source relate to characteristics of light emitted by thelight emitter and relate to geometrical parameters of the light source.In an optional embodiment of the method 100, the method 100 furthercomprises the stages of iv) obtaining 106 a second image of anilluminated environment being illuminated by the light source by meansof a second camera, wherein the first image is obtained from a firstposition in a first direction and the second image is obtained from asecond position in a second direction being different from the firstdirection, and v) obtaining 108 second camera settings, wherein thesecond camera settings represent parameters of an image processingsystem and of an optical system of the second camera used at the momentin time when the second image was obtained, wherein, in the stage 110 ofanalyzing the first image and analyzing the first camera settings, thesecond image and the second camera settings are also analyzed toestimate second parameters of the light source and to more accuratelyestimate the first parameters of the light source, wherein the secondparameters of the light source relate to characteristics of a light beamemitted by the light source. The second parameters comprise, forexample, information relating to a shape of the light beam emitted bythe light source.

The operation of the stages 102 to 110 is explained in more detail withFIG. 2 and FIGS. 3 a, 3 b. FIG. 2 presents an interior 200 of a room.The room is just an example, other rooms or spaces, or even outdoorspaces, may also be the area in which the method of characterizing alight source is used. At a ceiling 202 of the room is provided a lightsource 204. The light source 204 has a square size and comprisesanti-glare lamella in front of a light emitter of the light source 204.The light source 204 emits a light beam 206 in a downward direction. Asan example, a cylindrical object 216 is positioned in the room.

In an example, a first camera 208 obtains a first image from the lightsource from a first position P₁ in a first direction 210. In FIG. 3 anexemplary first image 300 is shown. As discussed previously, the firstcamera comprises an optical system and image processing system and atthe moment of obtaining the first image 300 specific parameters of theoptical system and the image processing system are adapted to specificvalues such that the obtained image is a relatively good image. A usermay influence the values of the parameters, or the first camera 208 mayautomatically adapt the values of the parameters to obtain therelatively good image. Relatively good means that the object is imagedin the first image 300 with a relatively good color balance, arelatively good contrast, a relatively good intensity level, and isoptionally also imaged sharply in the first image 300. Examples of suchparameters of the camera are shutter speed, aperture size, ISO value,parameters of color corrections, white balance parameters, focal pointof lens system, etc. The actual values of these parameters are read outto obtain the first camera settings.

Subsequently, the first image 300 is analyzed, together with theanalyzing the first camera settings, to estimate the first parameters ofthe light source. In the first image a bright area 302 may be seen withvertical dark lines. Around the bright area is a more dark area 306.While analyzing the first image 300, bright areas 302 are found whichrelate to the light emitting surface of the light emitter of the lightsource and/or to reflectors of the light source which reflect the lightemitted by the light emitter towards the camera. The color and intensityof the pixels of the bright area 302 comprise information aboutcharacteristics of the light that is emitted by the light emitter of thelight source 204. In order to transform a value of, for example, areceived light flux at the lens of the first camera 208 into firstparameters of the light source, in addition to the image the firstcamera settings must be analyzed because, if the shutter speed wasrelatively fast, the received light flux was relatively high. If theaperture size was relatively large, the received light flux wasrelatively low. Skilled persons in the field of light and optics arecapable to apply formulas, calculations, heuristics and/or algorithms totransform the information of the pixels of the first image 300 and thefirst camera settings towards information about the light that has beenemitted by the light emitter of the source. Examples of suchcharacteristics are emitted light intensity, light emission spectrum,color point of the emitted light, color temperature of the emittedlight. Reference is made to the articles “Measuring Luminance with aDigital Camera”, by Hiscocks, P. D. of Syscomp electronic DesignLimited, and published via the internethttp://www.ee.ryerson.ca:8080/˜phiscock/astronomy/light-pollution/luminance-notes.pdf.This article describes how a digital camera can be used to measure aluminance of a light source and how camera settings must be taken intoaccount.

Further, in the stage of analyzing 110 optionally geometrical parametersof the light source are obtained, such as, for example, shape of lightemitting surface, size of the light source 204, parameters of visibleoptical elements in the light source 204 (such as the anti-glare lamellaof the example), characteristics of the luminaire in which the lightsource 204 is provided. The characteristics of the luminaire comprise ashape, a size, a mounting and a type of luminaire. Pattern recognitiontechniques and geometrical transformations of the first image 300 of thelight source 204 may be used to obtain these geometrical parameters.

The well-visible dark lines 304 relate to an object which block thelight transmission and may be recognized as optical elements visiblefrom the first position P₁. Pattern recognition techniques may be usedto determine what kind of optical element is provided in the lightsource 204.

Alternatively, or additionally, in the stage of analyzing the firstimage 300 and the first camera settings, a database is consulted whichcomprises images of light sources. This database stores the images ofthe light sources accompanied by parameters of these imaged lightsources. Pattern recognition techniques and image comparison techniquesmay be used to find in the database a light source that might, with arelatively high probability, be imaged in the first image 300. The firstparameters of the light source are subsequently retrieved from thedatabase.

As can be seen in FIG. 1, in an optional embodiment, the method 100comprises also the stages of i) obtaining a second image in stage 106,and ii) obtaining second camera settings in stage 108. In the stage 110of analyzing the first image and analyzing the first camera settings,second image and the second camera settings are also analyzed toestimate second parameters of the light source and to more accuratelyestimate the first parameters of the light source, wherein the secondparameters of the light source relate to characteristics of a light beamemitted by the light source.

In FIG. 2 a second camera 215 is shown at the second position P₂, andthe second camera 215 may obtain the second image in the direction 214.As shown, the second camera 215 is able to image the room when it isilluminated by the light source 204. The direction 214 is not equal tothe first direction 210. Alternatively, the first camera 208 comprises asecond camera system which is able to obtain the second image fromsubstantially the same first position P₁ in a second direction 212 thatis substantially opposite to the first direction 210. For example, thefirst camera 208 is incorporated in a mobile phone or tablet computerwhich comprises the first camera 208 at a first side and which comprisesa second camera at a second side that is opposite the first side. Thefirst camera 208 may also be a digital camera with only a single camerasystem (optical system, etc.) and after obtaining the first image 300, auser turns around the first camera 208 at the first position P₁ toobtain the second image 350 in the second direction 212.

It is relatively difficult to detect information about specificcharacteristics of the light beam 206 of the light emitted by the lightsource 204 in the first image 300 only. Such specific characteristicsare, for example, spatial light emission distribution and spatial lightintensity distribution. The first image 300 does not show how wide ornarrow the light beam 206 is and does not show how the light intensitiesvary at different light emission directions because the first cameramainly receives at the first position P₁ only small portion of the lightthat has been emitted by the light source 204. The second image, eithertaken by the second camera 215 from the second position P₂ into thedirection 214 or taken by the first camera 208 form the first positionP₁ into the second direction 212, registers reflected light and as suchthere is information in the second image that relates to the light beam206.

An exemplary second image 350 is shown in FIG. 3 b. The second image 350is taken by the first camera 208 from the first position P₁ into thesecond direction 212. Thus, the second image 350 images the lightreflection pattern of the floor of the room 200 and the light reflectionby the top surface of the object 216. In second image 350 a relativelybright square 352 with a less bright area 354 around it can be seen. Therelatively bright area 352 is a footprint of the light beam 206 of thelight source 204. Such areas may be recognized in the analyzing step 110and based on the shape of the footprint of the light beam 206, a spatiallight emission distribution may be estimated, for example, that thecross-sectional shape of the light beam 206 has a substantially squareshape and that the light source 204 emits light up to a specific lightemission angle with respect to a normal to the ceiling (and, thus, withrespect to the light emitting surface of the light source 204). For thedetermination of the light emission angle, the position P₁ of the firstcamera may be taken into account. The less bright area 354 provides moreinformation about the spatial light intensity distribution of the lightbeam 206. In the analysis it is found that the light source 204 emitslower light intensities at larger light emission angles. Patternrecognition techniques, and finding relations, e.g. correlations,between the imaged light source in the first image 300 and the imagedshapes 352, 354 in the second image 350 may lead to the conclusion thatthe light beam has a substantially square cross-sectional shape. Whenthe estimated shape of the light source 204 as imaged in the first image300 and information of the second image 350 are correlated to eachother, the brightest circle 356 may be identified as an area of thesecond image 350 that is most probably not related to the light beam 206of the light source 204, but is most probably a surface of an object.This is furthermore confirmed by the dark area 358 which seems to be ashadow. Pattern recognition techniques may be used to detect shadows ofobjects. The shadows provide a lot of information about the light sourcecharacteristic such as, for example, a diffusiveness of the light of thelight beam 206. For example, if the shadow 358 gradually becomes lessdark, the light of the light beam 206 is relatively diffuse (whichmeans: within the light beam 206, light is emitted in severaldirections). When the borders of the shadow 358 are relatively sharp,the light in the light beam 206 is not diffuse, which means that, whenthe light beam is subdivided into sub-portions, almost all light rays ofa sub-portion are emitted in substantially the same direction.

Thus, the analysis of the second image 350 results in the estimation ofsecond parameters that are characteristics of the light beam 206 emittedby the light source 204. The information of the second image 350 mayalso be used to more accurately estimate the first parameters. Forexample, if in the second image 350 the illuminated environmentreflects, within certain accuracy levels, about the same color of light,this color of the reflected light strongly relates to the color of lightemitted by the light source. Thus, the reflected light may be used tofine tune estimated parameters of the light emitted by the light source204. It is to be noted that it may also work the other way around. When,based on the first image, the color of the emitted light is known, thereflected light as present in the second image may be used to estimatecolors of surfaces of the illuminated environment.

It is to be noted that, when the second image 350 is not taken from thefirst position P₁ and/or not in the second direction 212, the secondimage 350 looks differently and geometrical transformation techniquesmay be used to transform the second image into an image that is similarto the image of FIG. 3 b. However, transforming the second image in sucha similar image is not always necessary, because, while analyzing thesecond image to obtain the second parameters of the light source, thegeometrical relations between the information present in the secondimage and the direction of the light beam emitted by the light source204 may already be taken into account.

FIG. 1 further presents sub-stages of the stage 102 of obtaining thefirst image 300. In stage 112, the user is instructed to direct thefirst camera to the light source. When, as will be discussed later inthis application, images of other light sources must be made, the useris instructed to direct the first camera towards the other lightsources. In stage 114, the first camera detects on basis of informationof the image processing system whether the amount of received lightexceeds a minimum value. This minimum value may be predetermined, or maybe varies according to environmental conditions (such as, for example,the average lighting conditions of the environment). Determining theamount of received light comprises, for example, integrating thelighting intensity over an area of an image sensor of the first cameraand applying corrections for, e.g., the aperture size and focaldistance. In stage 116, the respective image is obtained with the firstcamera when the amount of the received light exceeds the minimum value.Optionally, stage 106 comprises sub-stages in which the user isinstructed to move the first camera or the second camera towards theilluminated environment.

It is to be noted that in an optional embodiment, the first cameraand/or the second camera register mainly light in a spectral range thatis visible to the human naked eye. In another embodiment, the firstcamera, and optionally the second camera, is also configured to imagethe light source in the infrared spectral range (besides imaging thelight source in the visible spectral range) to obtain a heat signatureof the light source. In this embodiment, the stage 102 of obtaining thefirst image also comprises obtaining the heat signature, and the stage110 of analyzing the first image and the first camera settings alsocomprises analyzing the heat signature to (more accurately) estimatefirst parameters and/or second parameters. For example, when the lightsource 204 comprises an incandescent lamp, the heat profile may provideinformation about the possible temperature of a filament, which oftenrelates to the use of specific materials in the filament itself and/orthe use of specific gasses in the incandescent lamp. For example, thetraditional light bulb and halogen lamps are embodiments of incandescentlamps. However, other materials are used in these lamps resulting in,for example, other heat signatures—consequently, different heatsignatures can be used to distinguish between, for example, thetraditional light bulb and halogen lamps.

In an optional embodiment, the first camera and/or the second camera area hyper spectral camera. Conventional cameras create an image of theelectromagnetic waves that are received in the spectrum that is visibleto the human naked eye. A hyper spectral camera collects and processesinformation in more ranges of the complete electromagnetic spectrum.Examples of such additional ranges of the electromagnetic spectrum inwhich information is collected and processed are for example theinfrared spectral range and the near Ultra Violet spectral range. Ahyper spectral camera generates, in specific embodiments, differentimages for different spectral ranges. Hyper spectral cameras are capableof collecting more information and if more information is obtained,characteristics of the light source can be estimated more accurately.All information obtained by or portions of the information obtained bythe hyper spectral cameras may be used in the stage 110 of analyzing thefirst image and the first camera settings to (more accurately) estimatefirst parameters and/or second parameters. For example, electromagneticwaves emitted at other wavelengths than the wavelengths of the visiblespectral range provide information about the materials used in the lightemitter of the light source. They may also reveal that some UVwavelengths responsible for black light effects are present in the lightemission.

In FIG. 2 a second light source 218 has been drawn which alsoilluminates a portion of the room 200. If we assume that this secondlight source 218 has been switched on, the second image 350 of FIG. 3 bwould look differently and more resemble the second image 400 of FIG. 4a. In the second image 400 it is seen that there are two bright areas,formed by square 352 and ellipse 402. Also a second shadow may be seen404. In an optional embodiment of the method, the second image 400 isalso analyzed to determine whether the illuminated environment isilluminated by additional light source. This stage 452 of analyzing thesecond image to find additional light source 452 may be subdivided intothe stages of: detecting an object 356 in the second image 400 in stage460, detecting shadows 404, 356 around the detected object 356 in stage462, and analyzing the detected shadows 404, 356 to estimate whether theilluminated environment is illuminated by additional light sources instage 464. In a further optional embodiment, the number of detectedlight sources is communicated to the user such that the user can confirm(or change) the number of light source that were in use at the momentwhen the second image was obtained.

Subsequently, when it has been detected that the illuminated environmentis illuminated by additional light source(s), additional first imagesfrom the additional light source(s) 218 are obtained in stage 454, andadditional first camera settings are obtained in stage 456. Theadditional first camera settings represent the parameters of the imageprocessing system and of the optical system of the first camera used atthe moment of time when the additional first images were obtained.Subsequently, in an optional stage, the additional first image and theadditional first camera settings are analyzed in stage 458 to estimateadditional parameters of the additional light sources. The additionalparameters of the additional light sources relate to characteristics oflight emitted by the additional light emitters and relate to geometricalparameters of the additional light sources. The additional first imagesand the additional first camera settings are also taken into account inthe stage 110 of analyzing the first image and the first camera settingsand the second image and the second camera settings, to estimate thefirst parameters and/or the second parameters more accurately. Forexample, when it is known that the additional light source emits aspecific color, it can be seen from the second image 400 how thisadditional light source influences the imaged illuminated environment.Determining the influence of the additional light sources leads to moreknowledge about the lighting effects in the illuminated environment,such that in the step 110 of analyzing, the lighting effect of the lightsource 204 on the illuminated environment can be better isolated fromall other visible light effects.

FIG. 5 a presents additional stages 500 which may be added to the method100 of FIG. 1. The additional stages 500 relate in particular tosituations in which the light source may operate in differentoperational modes wherein the light source emits a different lightemission in each one of the operational modes. For example, the lightemitter may be controlled in a first operational mode wherein it emits100% of a maximum light intensity, and may be controlled in a secondoperational mode wherein it emits 50% of the maximum light intensity. Itis to be noted that the operational modes may also relate to theemission of different color spectra, like more warm white light or morecool white light, or that the different operational modes may alsorelate to the emission of different light beams, like a more wide lightbeam or a more narrow light beam. It is further to be noted that in thecontext of this document “operational mode” relates to a mode wherein atleast some light is emitted and does not relate to the “off” state ofthe light source. It is further assumed that the first image is taken instage 102 when the light source was operating in the first operationalmode. The additional stages are: controlling the light source to operatein the second operational mode in stage 502, obtaining a further firstimage of the light source in operation in the second operational mode bymeans of the first camera in stage 504, obtaining further first camerasettings in stage 506, and analyzing the further first image andanalyzing the further first camera settings to estimate furtherparameters of the light source in relation to the second operationalmode in stage 508. The further parameters of the light source relate tocharacteristics of light emitted by the light emitter and relate togeometrical parameters of the light source and the further first camerasettings represent the parameters of the image processing system and ofthe optical system of the first camera used at the moment in time whenthe further first image was obtained.

FIG. 6 a presents an example of a further first image 600 which isobtained in stage 504. In this example it is assumed that the furtherfirst image 600 of the light source 204 is obtained from the firstposition P₁ in the first direction 210 (see FIG. 2) and that the lightsource 204 is operating in a second operational mode in which the lightsource 204 emits a lower light intensity. The relatively bright square602 in the middle of the image is less bright than the square 302 of thefirst image 300 of FIG. 3 a which indicates that the light source 204emits a lower light emission in the second operational mode. In anotherembodiment, the further first image 600 is almost the same as the firstimage 300 of FIG. 3 a (which means that square 602 has almost the samebrightness as the square 302 of the first image 300), but the furthercamera settings indicated that the shutter time was longer, that theaperture size was larger, and/or that the ISO value was higher. In thatsituation, in the stage 508 of analyzing the further first image and thefurther first camera settings, the combination of the further firstimage 600 and the further first camera settings immediately provide theinformation that the light source 204 emits in the second operationalmode less intense light and the combination of the further first image600 and the further first camera settings can be used to estimate theactual amount of light that is emitted by the light source in the secondoperational mode (as well as other parameters may also be estimated onbasis of this information).

FIG. 5 b presents additional stages 550 which may be added to the method100 of FIG. 1. The stages 550 provide to the user a method whichcharacterizes a light source and which proposed to the user areplacement light source or replacement light emitter. It is assumedthat a list with replacement light sources and/or replacement lightemitters is available and that, together with the replacement lightsources and/or replacement light emitters, parameters are stored. Suchparameters provide information about for example the operational modesand characteristics of the light emitted by the replacement light sourceand/or light emitter, and/or for example characteristics of the lightbeam emitted by the replacement light sources and/or light emitters.This list may be available in a database and accessible by the methodstages 550. The additional stages 550 at least comprise the stages of:i) selecting in stage 552 from the list of replacement light sourcesand/or replacement light emitters a replacement light source and/or areplacement light emitter, wherein the replacement light source and/orthe replacement light emitter has at least one parameter that is similarto one of the first parameters and/or the second parameters of the lightsource, ii) proposing in stage 554 the selected replacement light sourceand/or the selected replacement light emitter to a user. It is to benoted that one similar parameter should be enough for selecting thereplacement light source and/or the replacement light emitter. However,in an embodiment the replacement light emitter and/or replacement lightsource is selected which has a relatively large number of parameterswhich are similar to first parameters and/or second parameters of thelight source. Optionally, the replacement light emitter and/orreplacement light source is selected which has most parameters in commonwith the first parameters and/or the second parameters of the lightsource. In an optional embodiment, when the light source has differentoperational modes, the further parameters are also taken into accountand the proposed replacement light source and/or replacement lightemitter has also such an additional operational mode with similarparameters in this additional operational mode. Proposing thereplacement light source and/or light emitter may be done via a displayand/or user interface of, for example, the first or second camera, ordevice of a system executing the method according to the invention.

In an embodiment, the additional stages 550 may also comprise the stagesof: iii) simulating in stage 556 an influence of the selectedreplacement light source and/or the selected replacement light emitteron the illuminated environment, iv) creating in stage 558 an adaptedsecond image showing the result of the simulation in stage 556 on theenvironment, v) presenting in stage 560 the adapted second image to theuser. When a light source is replaced, it is often not possible toobtain a replacement light source and/or replacement light emitter whichcomprises exactly the same parameters as the light source. Before theuser decides to replace the light source, it may be advantageous to showto the user the effect of the replacement, as provided by the aboveadditional stages iii) to v). The presenting of the adapted second imagemay be done via a display and/or user interface of, for example, thefirst or second camera, or a device of a system which runs the methodaccording to the invention.

Several methods are known in the art to simulate the effect of a lightsource and/or light emitter on an environment. For example, in thearticle “Application of RELUX software in Simulation and Analysis ofEnergy Efficient Lighting Scheme”, Shailesh, K. R. et al, InternationalJournal of Computer Applications, Vol 9, No 7, November 2010, discussesthe application of such automatic methods in a specific case study.Another article which describes such methods is “Advanced LightingSimulation Tools for Daylight purposes: Powerful Features and RelatedIssues”, Bhavani R. G., et al, Trends in Applied Sciences Research, Vol.6, Issue 4, 2011 Lighting or illumination effects of the light sourcecan be recognized in the illuminated environment (as imaged in thesecond image) by using, for example, the first parameters and the secondparameters of the light source, after which the recognized lighting orillumination effects can be replaced by lighting or illumination effectsof the replacement light source and/or replacement light emitter. Thegeneration of the lighting or illumination effects of the replacementlight source and/or replacement light emitter may be done on the basisof parameters of the replacement light source and/or replacement lightemitter that can be obtained from a list or database with replacementlight sources and/or replacement light emitters.

In an embodiment, the simulation stage 556 of the influence of theselected replacement light source and/or the selected replacement lightemitter and the creation stage 558 of the adapted second image may beperformed by the subsequent steps: (i) the second image is decomposed inthree sub-images which relate each to a color channel (red, blue andgreen), (ii) subsequently adjustment ratios are calculated for eachcolor channel (red, blue and green) wherein the adjustment ratiosrepresent the amount of light in the color channel emitted by theselected replacement light source and/or the selected replacement lightemitter divided by the amount of light in the color channel emitted bythe light source, (iii) multiplying the values of the pixels of eachsub-image (representing one specific color channel) with the adjustmentratio for that specific color channel to obtain adapted sub-images, andfinally (iv) the adapted second image is created by combining theadapted sub-images. It is to be noted that decomposing an image intodifferent sub-images representing specific color channels and combiningadapted sub-images into the adapted image is well-known to the skilledperson—almost every image processing program is capable of performingthe decomposition and combining steps.

It is to be noted that the steps of simulating 556, creating 558 andpresenting 560 the adapted second image may also be performed fordifferent operational modes of the selected replacement light sourceand/or the selected replacement light emitter.

It is further to be noted that, additional second images of theilluminated environment may be obtained from the second position P₂ inthe direction 214, or from the first position P₁ in the second direction212. The additional second images are obtained when the light source isswitched off and/or when the light source operates in anotheroperational mode. The additional second images of the illuminatedenvironment may be used to determine the effect of the light source 204on the illuminated environment such that, when a replacement lightsource and/or replacement light emitter is proposed, the effect of theproposed replacement light source and/or replacement light emitter canbe accurately simulated such that a relatively good adapted second imagecan be obtained. When, for example, an image is taken of the illuminatedenvironment at the moment in time when the light source 204 was switchedoff, thereby providing a base line image of the environment notilluminated by the light source, and knowing the first and secondparameters of the light source 204, then there are methods known in theprior art to estimate/simulate what the effect of the light source 204on the illuminated environment will be. In a further refinement of themethod steps used to simulate the influence of a selected replacementlight source and/or a selected replacement light emitter and create anadapted second image, as described in previous paragraphs, the methodmay further use the base line image of the environment not illuminatedby the light source as an offset in the pixel calculations of the red,green and blue sub-images. For example, if the base line image is firstsubtracted from the second image, for example by pixel-wise subtractionof the decomposed base line RGB sub-images from the decomposed secondRGB sub-images, then the adjustment ratio(s) only takes into account theillumination of the light source and the replacement light source andsubstantially eliminates the contribution of other light sources 218 ordaylight in the calculations of the adjustment ratio(s) and the adjustedsecond image.

FIG. 6 b presents an example of an adapted second image 650 which is theresult of the additional stages 550. When, for example, the selectedreplacement light source and/or selected replacement light emitter emitsa different color of light than the light source 204 of FIG. 2, theadapted second image 650 looks differently than the second image 350 ofFIG. 3 b. The top surface 656 of the object is imaged in a differentcolor, and the footprint of the light beam 652/654 has another color.When, in an example, the selected replacement light source and/orselected replacement light emitter emits a different shaped light beam,the shape of the footprint 652/654 would have been different.

FIG. 7 presents a mobile device 700 according to the second aspect ofthe invention. The front side 704 is presented at the left and the rearside 754 is presented at the right. The mobile device 700 comprises atleast a processing unit 702, a data storage 703 and a first camera 756.The first camera 756 comprises an image processing system (not shown)and an optical system (not shown) of which, during obtaining an imagewith the first camera, parameters are automatically adjusted by thefirst camera 756 to obtain a quality image of an imaged object orenvironment. Such parameters are discussed previously and may includeshutter speed, focal distance, aperture size, image sensor sensitivity,color correct, color balance, etc. The data storage 703 stores acomputer program comprising computer program code adapted to perform thestages of one of the above discussed embodiments of the method ofcharacterizing a light source according or one of the above discussedembodiments of the method of selecting a replacement light source. Thefirst camera 756 is coupled to the processing unit 702 and theprocessing unit 702 is coupled to the data storage 703. The processingunit 702 may be adapted to execute the computer program as stored on thedata storage 703. The data storage may comprise any data storage mediumsuch as, for example, a hard disk, volatile or non-volatile memory, etc.

The mobile device 700 optionally comprises a second camera 706 which isarranged at the front side 704 of the mobile device 700. The secondcamera is also coupled to the processing unit 702 and the second cameraalso comprises an image processing system and an optical system ofwhich, during obtaining an image with the second camera 706, parametersare automatically adjusted by the second camera 706 to obtain a qualityimage of an imaged object or environment. The second camera 706 obtainsimages in a second direction which is substantially opposite a firstdirection in which the first camera 756 obtains images.

The first side 704 of the mobile device 700 optionally comprises adisplay 786 and an input means 710 for receiving user input. The inputmeans 710 is, for example, a push button, or, for example, a touch padwhich registers movements of a finger of a user when the user moves thefinger over the input means 710, or a keypad. In another embodiment, thedisplay 786 is constituted by a touch display on which user input may bereceived.

The mobile device 700 may further comprise a computer program whichcomprises instructions to instruct a user of the mobile device to obtainthe first image of the light source with the first camera. The computerprogram comprises computer program code, i.e. instructions, foroperating the display 786 to instruct the user of the mobile device 700.Optionally, the computer program may further comprise instructions topresent the obtained first image on the display 786. Optionally, whenthe mobile device 700 only comprises one camera (for example only thefirst camera 756) the computer program comprises instructions toinstruct the user to direct the mobile phone in a substantially oppositedirection to obtain the second image of the illuminated environment.Optionally, the computer program instructs the processing unit topresent the obtained second image on the display 786. Further, when themethod that is implemented in the computer program proposes areplacement light source and/or replacement light emitter, the proposalis communicated to the user via the display 786. Optionally, in oneembodiment the mobile device 700 comprises an internal database withreplacement light source and/or replacement light emitters and inanother embodiment, the mobile device 700 comprises a network interfacefor connecting to a network which is coupled to a database withreplacement light source and/or replacement light emitters. In yetanother embodiment, the method that is implemented in the computerprogram that is stored on the mobile device 700 simulates the effect ofa proposed replacement light source/light emitter and presents anadapted second image on the display 786.

It is to be noted that the mobile device 700 is just an example of adevice which may be configured to perform the method according to thefirst aspect of the invention. Another type of device, such as atraditional computer with a display and a webcam, may also be capable ofperforming the method according to the invention when provided with theright program code.

Additional embodiments are discussed hereinafter:

Constant Illumination State Embodiment.

Here a first system comprises of a mobile device incorporating either asingle forward facing camera, or both forward facing and rear facingcameras. The mobile device may optionally include a gyroscope,accelerometers and processing means which may be used to provide anInertial Navigation System (INS) capability. The image sensor(s) andassociated processing system incorporates a capability whereby theeffective aperture, speed, ISO and other characteristics may be varied.The mobile device is connected—through a wireless connection—eitherdirectly or indirectly to a server comprising of a processor, memory andcommunications interfaces.

A method may be executed on the system as follows (for mobile deviceswith both forward and rear facing image sensors):

1. User, or another application, selects “Light source replacementmobile device application diagnostic.2. The user is instructed to image the lamp providing the source ofillumination and/or the scene of illumination using the forward facingand rear facing image sensors of the mobile device,3. The user images the light source and/or scene of illumination,4. The mobile device analyses the image to check that the probabilitythat a light source is being imaged exceeds a threshold value,5. The mobile device captures image from both forward and rear facingimage sensors, automatically adjusting the aperture, speed, focus andother settings to be consistent with the images being captured. Thesettings are stored with the images as metadata.6. Optionally, the image of the illuminated scene is analysed todetermine whether there are shadows which may suggest the existence ofmore than one source of illumination. If shadows exist, then these arefurther analysed to determine the likely number of light sources.Through an iterative process starting each time from step 2 the user isadvised of the number of remaining light sources to be imaged and askedto confirm that the value is correct. This is repeated until allpossible light sources have been imaged.7. The captured image of the light source is analysed by a suitablealgorithm to determine the possible likely type, size, power and shapeof the light source. For example, it is determined whether the lightsource is a point (LED, halogen spotlight etc.) or a panel (OLED,fluorescent tube etc.). Further diagnosis is made using the metadata forthe image, together with the image data, to determine likely power,technology type, distance from camera etc. These may then be used tofilter a list of all possible lamp types to produce a shorted list fromwhich the user may then be invited to select the actual lamp type. Theoutput from step 7 is a set of values which indicates the properties ofthe lamp. These may include technology type, power, shape etc.8. This lamp data is then associated with the captured image of thescene, and stored either locally on the mobile device or/andcommunicated to the server.9. Using the lamp data from (8), algorithms can be used to simulate theeffect of a new lamp (of known attributes) being used to replace theoriginal lamp whose data is captured in 8. A representation of the newscene may be computed based on the characteristics of the new lamp, andthis displayed to the user using the display of the mobile device.

Alternatively, in between the above presented steps (5) and (6) the useris guided to take an image of the illuminated scene. This is achieved byusing the INS of the mobile device, which guides (through audible,visual, haptic or other interfaces) the user to rotate the devicethrough 180 degrees about an axis. Steps 3 to 5 are then repeated, butwith the illuminated scene replacing the source of illumination.

Varying Illumination State Embodiment.

Here the system comprises of a mobile device incorporating either asingle forward facing camera, or both forward facing and rear facingcameras. The mobile device may optionally include a gyroscope,accelerometers and processing means which may be used to provide anInertial Navigation System (INS) capability. The image sensor(s) andassociated processing system incorporates a capability whereby theeffective aperture, speed, ISO and other characteristics may be varied.The mobile device is connected—through a wireless connection—eitherdirectly or indirectly to a server comprising of a processor, memory andcommunications interfaces. The lamp which is being imaged has a means ofcontrol, either through a manual switch or in an automated way through acontrol system which optionally may have connectivity to the mobiledevice.

A method may be executed on the system as follows (for mobile deviceswith both forward and rear facing image sensors):

1. User, or another application, selects “Light source replacement”mobile device application diagnostic,2. The number of lamp states, n, for the operation is determined.3. The lamp state is set to State (A+iteration number, e.g. A₁, A₂ . . .A_(n)) by manual or automatic means4. The user is instructed to image the lamp providing the source ofillumination and/or the scene of illumination using the forward facingand rear facing image sensors of the mobile device,5. The user images the light source and/or scene of illumination,6. The mobile device analyses the image to check that the probabilitythat a light source is being imaged exceeds a threshold value,7. The mobile device captures image from both forward and rear facingimage sensors, automatically adjusting the aperture, speed and othersettings to be consistent with the images being captured. The settingsare stored with the images as metadata.8. Steps 3 through 7 are repeated until each of the lighting states hasbeen captured.9. Optionally, the images of the illuminated scene are analyzed todetermine whether there are shadows which may suggest the existence ofmore than one source of illumination. If shadows exist, then these arefurther analyzed to determine the likely number of light sources.Through an iterative process starting each time from step 2 the user isadvised of the number of remaining light sources to be imaged and askedto confirm that the value is correct. This is repeated until allpossible light sources have been imaged.10. The captured images of the light source are analyzed by a suitablealgorithm to determine the possible likely type, size, power and shapeof the light source. For example, it is determined whether the lightsource is a point (LED, halogen spotlight etc.) or a panel (OLED,fluorescent tube etc.). Further diagnosis are made using the metadatafor the image, together with the image data, to determine likely power,technology type etc. These may then be used to filter a list of allpossible lamp types to produce a shorted list from which the user maythen be invited to select the actual lamp type. The output from step 10is a set of values which indicate the properties of the lamp. These mayinclude technology type, power, shape etc.11. This lamp data is then associated with the captured image of thescene, and stored either locally on the mobile device or/andcommunicated to the server.Using the lamp data from (11), algorithms can be used to simulate theeffect of a new lamp (of known attributes) being used to replace theoriginal lamp whose data is captured in 11. A representation of the newscene may be computed based on the characteristics of the new lamp, andthis displayed to the user using the display of the mobile device.

Non mobile device image sensors may also be used in some circumstances.These may, for example, include webcam links which are embedded in atelevision. In this instance, additional processing and/or differentmethod will be necessary as this will only image from one position.

Other permutations of the previously discussed embodiments are possible,for example with INS and only a single sensor as in the Constantillumination state example.

In summary: A method of and a device for characterizing a light sourceand a method of selecting a replacement light source are provided. Themethod obtains a first image of a light source in operation, obtains asecond image of the illuminated environment, and obtains first camerasettings and second camera settings of the optical system and imageprocessing system of the respective first and second camera at therespective moments in time that the first image and the second image wasobtained. The first image, the second image, and the first and secondcamera settings are analyzed to estimate characteristics of the lightsource. The characteristics of the light source may be used to propose areplacement light source and characteristics of the proposed replacementlight source may be used to simulate the effect of the replacement lightsource on the illuminated environment.

It should be noted that the above-mentioned embodiments illustraterather than limit the invention, and that those skilled in the art willbe able to design many alternative embodiments without departing fromthe scope of the appended claims.

In the claims, any reference signs placed between parentheses shall notbe construed as limiting the claim. Use of the verb “comprise” and itsconjugations does not exclude the presence of elements or steps otherthan those stated in a claim. The article “a” or “an” preceding anelement does not exclude the presence of a plurality of such elements.The invention may be implemented by means of hardware comprising severaldistinct elements, and by means of a suitably programmed computer orprocessing unit. In the device claim enumerating several means, severalof these means may be embodied by one and the same item of hardware. Themere fact that certain measures are recited in mutually differentdependent claims does not indicate that a combination of these measurescannot be used to advantage.

1. A method of characterizing a light source, the light sourcecomprising a light emitter for emitting light, the method comprises thestages of obtaining a first image of the light source in operation bymeans of a first camera, the first image is obtained from a firstposition (P1) in a first direction, obtaining first camera settings,wherein the first camera settings represent parameters of an imageprocessing system and of an optical system of the first camera used atthe moment in time when the first image was obtained, obtaining a secondimage of an illuminated environment being illuminated by the lightsource by means of a second camera, the second image is obtained from asecond position (P2) in a second direction different from the firstdirection, obtaining second camera settings, wherein the second camerasettings represent parameters of an image processing system and of anoptical system of the second camera used at the moment in time when thesecond image was obtained, analyzing the first image and analyzing thefirst camera settings to estimate first parameters of the light source,wherein the first parameters of the light source relate tocharacteristics of light emitted by the light emitter, wherein, in thestage of analyzing the first image and analyzing the first camerasettings, the second image and the second camera settings are alsoanalyzed to estimate second parameters of the light source and to moreaccurately estimate the first parameters of the light source, whereinthe second parameters of the light source relate to characteristics of alight beam emitted by the light source, the second parameters compriseinformation relating to a shape of the light beam.
 2. The methodaccording to claim 1, wherein the second camera is the first camera andthe method further comprising the stage of repositioning the firstcamera after obtaining the first image to the second position (P2) inthe second direction for obtaining the second image.
 3. The methodaccording to claim 1, wherein the second position (P2) is substantiallyidentical to the first position (P1) and wherein the second direction issubstantially opposite to the first direction.
 4. The method accordingto claim 1, wherein, characteristics of light emitted by the lightemitter comprise at least one of: emitted light intensity by the lightsource, light emission spectrum of the light source, color point of theemitted light, color temperature of the emitted light, and, optionally,the first parameters comprise geometrical parameters of the lightsource, geometrical parameters of the light source comprise at least oneof: shape of light emitting surface of the light source, size of thelight source, parameters of visible optical elements in the lightsource, characteristics of the luminaire in which the light source isprovided, the characteristics of the luminaire comprise a shape, a size,a mounting and a type of luminaire.
 5. The method according to claim 1further comprising the stage of: analyzing the second image to determinewhether the illuminated environment is also illuminated by additionallight sources, the additional light sources comprising additional lightemitters, obtaining additional first images of the additional lightsources, obtaining additional first camera settings, wherein theadditional first camera settings represent the parameters of the imageprocessing system and of the optical system of the first camera used atthe moment of time when the additional first images were obtained,wherein, in the stage of analyzing the first image and analyzing thefirst camera settings together with the second image and the secondcamera settings, the additional first images and the additional firstcamera settings are also analyzed to estimate the influence of theadditional light sources on the illuminated environment for moreaccurately estimating the second parameters and/or first parameters ofthe light source (204).
 6. The method according to claim 1 furthercomprises the stage of: controlling the light source into a secondoperational mode, wherein the light source is controllable in a firstoperational mode and the second operational mode, each one of the firstoperational mode and the second operational mode relates to a specificlight emission, the light emission of the first operational mode beingdifferent from the light emission of the second operational mode, andwherein the first image is obtained from the light source when the lightsource was operating in the first operational mode, obtaining a furtherfirst image of the light source in operation in the second operationalmode by means of the first camera, obtaining further first camerasettings, wherein the further first camera settings represent theparameters of the image processing system and of the optical system ofthe first camera used at the moment in time when the further first imagewas obtained, analyzing the further first image and analyzing thefurther first camera settings to estimate further parameters of thelight source in relation to the second operational mode, wherein thefurther parameters of the light source relate to characteristics oflight emitted by the light emitter and/or relate to geometricalparameters of the light source.
 7. The method according to claim 1,wherein the stages of obtaining the first image, obtaining theadditional first images, and/or obtaining the further first imagecomprise the stages of: instructing a user to direct the first camerato, respectively, the light source, the additional light source or thelight source operating the second operational mode, detecting on basisof information of the image processing system whether the amount ofreceived light exceeds a minimum value, obtaining the respective imagewhen the amount of received light exceeds the minimum value.
 8. Themethod according to claim 1, wherein the stage of analyzing the firstimage and analyzing the first camera settings to estimate the firstparameters of the light source comprises the stages of: comparing thefirst image with images of light sources stored in a database to find animage of a light source that is similar to the first image, the databasealso stores together with the images of the light sources informationabout the parameters of the respective light sources, obtaining thefirst parameters from the database by obtaining parameters of the lightsource of the found image that is similar to the first image.
 9. Themethod according to claim 1, wherein the first camera is also configuredto image the light source in the infrared spectral range to obtain aheat signature of the light source and the stage of obtaining the firstimage comprises obtaining a heat signature, and wherein in the stage ofanalyzing the first image and analyzing the first camera settings toestimate the first parameters of the light source, the heat signature isalso analyzed to obtain further characteristics of the light sourcewhich relate to the operational conditions of the light source.
 10. Themethod according to claim 1, wherein the first camera and/or the secondcamera are a hyper spectral camera.
 11. A method of selecting areplacement light source, the method comprises the stages of the methodof characterizing a light source according to claim 1 and comprises thefurther stages of: selecting from a list of replacement light sourcesand/or replacement light emitters a replacement light source and/or areplacement light emitter, wherein the replacement light source and/orthe replacement light emitter have at least one parameter that issimilar to one of the first parameters and/or the second parameters ofthe light source, proposing the selected replacement light source and/orthe selected replacement light emitter to a user.
 12. The method ofselecting a replacement light source according to claim 11 furthercomprising the stage of: simulating an influence of the selectedreplacement light source and/or the selected replacement light emitteron the illuminated environment, creating an adapted second image showingthe result of the simulating of the influence of the selectedreplacement light source and/or the selected replacement light emitteron the environment, presenting the adapted second image to the user. 13.The method of selecting a replacement light source according to claim11, wherein the selected replacement light source and/or the selectedreplacement light emitter may operate in a third operational mode and afourth operational mode, in each one of the third operational mode andthe fourth operational mode the selected replacement light source and/orthe selected replacement light emitter emits a specific light emission,the light emission of the third operational mode being different fromthe light emission of the fourth operational mode, and the obtainedadapted second image relates to the third operational mode of theselected replacement light source and/or the selected replacement lightemitter, the method further comprising the stages of: simulating aninfluence of the selected replacement light source and/or the selectedreplacement light emitter on the environment, the simulating relates tothe operation of the selected replacement light source and/or theselected replacement light emitter in the fourth operational mode,creating a further adapted second image showing the result of thesimulating of the influence of the selected replacement light sourceand/or the selected replacement light emitter on the environment,presenting the further adapted second image to the user.
 14. Adownloadable application for a mobile computing device, the downloadableapplication comprises a computer program comprising computer programcode adapted to perform the stages of the method of characterizing alight source according to claim 1 or of the method of selecting areplacement light source when the computer program is run on aprocessing unit of the mobile computing device.
 15. A device forcharacterizing a light source, the device comprising a first camera, thefirst camera comprising an image processing system and an optical systemof which, during obtaining an image with the first camera, parametersare adjusted to obtain a quality image of an imaged object orenvironment, a data storage storing a computer program comprisingcomputer program code adapted to perform the stages of the method ofcharacterizing a light source according to claim 1 or of the method ofselecting a replacement light, a processing unit being coupled to thefirst camera and being coupled to the data storage, the processing unitbeing configured to execute the computer program stored on the datastorage.